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60 GEMS AND PRECIOUS STONES.
The
greatest fault the amethyst has is that in artificial light it loses
apart of its beauty, appearing of a blackish hue. It harmonises
perfectly with gold and pearls, and no doubt will continue to increase
in popularity now that the taste for this gem has revived.
The
amethyst is found in numerous localities in the United States of
America, and in Mexico ; those from Gruanajuata, which have a
world-wide reputation, are found in large quantities, and range in
colour from the most delicate pink to the deepest red. The crystals are
frequently light in colour at the base, but much darker at the
termination. The colour of the amethyst can be removed hy heating, and
this treatment is carefully used to remove spots and faulty colouring
in a gem, as the stone is thus made of a uniform colour. This is a very
common mode of treatment to add to the colour of some gems, notably the
topaz and the Oriental carnelian. One method of "burning" precious
stone3 is to roll them up in a piece of sponge and burn them with it,
or, as is done with the amethyst, to place the stones in a crucible
with unslacked lime or iron filings, and heat them until they are quite
clear. The process requires the greatest care, or the gem may be
hopelessly destroyed.
Besides
the localities already mentioned, the amethyst is found in Spain,
India, Persia, Siberia, Hungary, Saxony, and Ceylon, in beautiful
crystals. Near Oberstein, in Germany, it is found in a trap rock, in
geodes in agate; these geodes being sometimes as much as 2 feet in
diameter, hollow, and filled with crystallized amethyst of a fine
colour. Similar geodes are found in other parts of the world. The
amethyst is found in many localities in New South Wales, but of little
value for cutting purposes. It is found in geodes in the basalt at
Kiama, also at Eden, Boggabri, Brewongle, Emmaville, and many other
places.
Agate.
This
is virtually a variegated chalcedony, composed of differently coloured
bands, sometimes with characteristic markings due to visible
impurities. Agate forming varieties of quartz consists, besides
chalcedony, of carnelian, jasper, quartz, and sometimes amethyst. Two
or more of these combined, and presenting a diversity of spots or
bands, form the agate ; and according to the distribution of these
bands or dendritic markings, so the stone is known by characteristic
names; it is called banded agate when the bands are delicate
parallel lines of while, pale or dark brown, or blackish colours,
sometimes a portion shows bluish and other shades. The lines are
generally wavy or circular. These bands are the edges of layers of
deposition, the agate having been formed by a deposit of silica from
solution intermittently supplied, in irregular cavities in rocks, and
deriving their concentric waving from the irregularities of the walls
of the cavity ; this variety is also known as ribbon agate, and when the colours are very sharply defined and a portion blackish, it is known as onyx agate. "When the variously coloured bands are in angular patterns it is known as fortification agate, from a supposed resemblance to the outlines of a fortification. Then we have other specimens known as jasper agate, and when resembling a breccia, as brecciated agate and others with fanciful names as zone agate, clouded agate, and wood agate. When the visible markings somewhat resemble moss enclosed, the specimen is known as moss agate or Mocha stone. This variety came originally from Arabia, but large quantities have been found in America.
The
beauty of the agate depends principally on the colour, brilliancy, and
character of the material forming the larger portion of the stone.
Besides being manufactured into articles for ornamental purposes, the
agate is a most useful stone in many other ways. It is made into
burnishers for the gilder, mortars are made of it for the pulverisation
of hard minerals in analysis, and
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